A robust verification protocol is an integral part of efforts to successfully denuclearize North Korea given what appears to be massive nuclear facilities the reclusive country has been operating for decades, a government source said Friday.

As South Korea and the United States are preparing to hold their respective summits with North Korea with denuclearization likely to top their agendas, how to verify the North's long running nuclear facilities draws keen attention as inspections and verification have served as a "deal breaker" in previous denuclearization talks.

The North kicked out inspectors of the International Atomic Energy Agency in 2009 and shortly thereafter it conducted its second nuclear test. Its nuclear facilities are believed to be mostly located in Yongbyon, but it is not clear what other clandestine nuclear facilities the North has been operating.

Yongbyon is a North Korean town housing a large-scale nuclear complex where experts say there are about 390 buildings, most of which are suspected of being related to the North's nuclear activities, according to experts.

"Verification is very important," the official told reporters on condition of anonymity. "Verification will emerge as a vital task when the North promises to give up its nuclear program and relevant agreements are reached."

The official said that a majority of those buildings and facilities in Yongbyon have not been looked into before, which would make it hard to verify what the North would declare under an agreement to give up its nuclear program.

"Without a robust verification protocol in place, (the North) could conceal anything it wants," the official said. "This explains why the declaration and verification process would be so important."

He, however, voiced cautious optimism, saying things could be different from the past as North Korean leader Kim Jong-un said he is willing to discuss denuclearization, setting in motion the current peace process from the top down.

"Our government will hold out cautious hope while making technical preparations in a careful and scrupulous manner," he said.

Citing previous global efforts that led to the denuclearization of such countries as South Africa, Libya and Iran to give up their pursuits of nuclear weapons development, he said it would be hard to pick any single method for North Korea.

He noted the government is instead working on how to find the merits of each mechanism and combine them to produce the most effective tool in dealing with the North's case.

"The government is doing its best to make the inter-Korean and U.S.-North Korea summits a success. Based on our previous experiences, we are making necessary preparations in a faithful manner without too much optimism or pessimism and determined not to lose those opportunities to help peace take root on the Korean Peninsula," he said.

The two Koreas will hold what will be their third summit in history next Friday, which will be followed by an unprecedented summit between the U.S. and North Korea either in May or early June.